1. Field of the Invention
The present invention generally relates to a lens, and more particularly to a fixed-focus lens.
2. Description of Related Art
FIG. 1 is a structural diagram of a conventional fixed-focus lens applied to a rear projection system as disclosed in U.S. Pat. No. 6,563,650. Referring to FIG. 1, the fixed-focus lens 100 includes a first lens group 110, a second lens group 120 and a third lens group 130 arranged in sequence from an object side to an image side. A light valve 50 is disposed on the image side. The first lens group includes four lenses 112, 114, 116 and 118. The second lens group 120 includes four lenses 122, 124, 126 and 128. The third lens group 130 includes five lenses 132, 134, 136, 138 and 139.
Because the conventional fixed-focus lens 100 uses a greater number of lenses, the production cost is also higher. In addition, the greater number of lenses also increases the overall length of the fixed-focus lens 100. Thus, when the fixed-focus lens 100 is applied to a rear projection television (RPTV), the RPTV will have a greater thickness. However, reducing the thickness of the RPTV will lead to various phenomena that affect the imaging quality such as an increase in the optical imaging aberration or even the appearance of ghost image.